Fix typo and explain the precedence of STDERR and STDOUT
What does this MR do?
Addresses comments https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5088#note_12884564
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Addresses comments https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5088#note_12884564